Mediator-Free Self-Powered Bioassay for Wide-Range Detection of Dissolved Carbon Dioxide

Electrochemical sensors for the dissolved CO₂ (dCO₂) measurement have attracted great interest because of their simple setup and the resulting low costs. However, the developed sensors suffer from the requirement of the external electrical power supply throughout the sensing. Here, the fabrication and evaluation of a self-powered biosensor based on biofuel cells (BFCs) for dCO₂ measurements are described. In this device, AuNPs-multiwalled carbon nanotubes/GOx-modified carbon paper (CP) served as a bioanode for the oxidation of glucose, while imine-linked covalent triazine framework (I-CTF)-modified CP was employed as the cathode for the reduction of Fe(CN)₆^3-. I-CTF is a porous organic polymer with a high CO₂ capture capacity. Voltammetry and electrochemical impedance spectroscopy confirmed that the electron transfer of Fe(CN)₆^3- on the I-CTF-modified electrode decreases after contacting I-CTF with dCO₂. In the designed BFC, by capturing CO₂ by the I-CTF-modified cathode, a significant decrease in open-circuit voltage (E^OCV) of the BFC was observed, which can be used for the sensitive measurement of dCO₂. In addition to the self-powering feature, the E^OCV of the BFC sensor can be restored when the captured CO₂ is desorbed from the I-CTF-modified cathode by increasing the temperature of the cathode. Finally, the BFC is integrated into a circuit containing a matching capacitor; the charges generated by the BFC are accumulated on the capacitor, and then the instantaneous current is quickly detected using a switching regulator and a digital multimeter. Under optimal conditions, the instantaneous current of the BFC sensor was found to sensitively respond to dCO₂ in a wide concentration range from 1.3 × 10^-5 to 0.252 atm with a low detection limit of 5 × 10^-6 atm.